1. Field of the Invention
The present invention relates to a lubricating grease composition and, in particular, to a grease composition for ball bearings.
2. Description of the Prior Art
As grease compositions used for bearings, in particular, those used in spindle motors for operating recording devices such as those for computer hard disks and CD-ROM's, there have conventionally been used, for instance, grease compositions, which comprise an ester oil such as dioctyl sebacate or a pentaerythritol ester, as a base oil and a thickening agent such as lithium stearate or lithium hydroxystearate. However, the acoustic life of these bearings has generally been insufficient. This is because the recording density of these devices has recently been increased and the increase in the recording density in turn requires the improvement of the precision of bearings and an increase in the number of revolutions of such motors. The latter would be accompanied by an increase in the temperature of bearings during practical use.